1. Field of the Invention
The present invention relates to a technique of sequentially transmitting images generated in an information processing apparatus at a predetermined interval and presenting them by an image output apparatus.
2. Description of the Related Art
Recent popularization of image output apparatuses such as a projector makes it possible to output image signals by connecting an information processing apparatus such as a PC to the projector, and present images generated by the PC to many people so that they can view the images in a presentation or the like. The connection between the PC and the projector generally uses analog connection via an analog RGB cable, and allows smooth continuous image presentation by outputting analog image signals generated by the PC in synchronism with clock signals, as needed.
However, the connection between the PC and the projector using the cable suffers the preparation of the cable, the labor of connection when the connection is switched between a plurality of PCs to use the project, and a problem in connection such as spatial limitation in the use of the PC. That is, image presentation using the projector has various restrictions imposed by the use of physical wiring.
To solve this, a projector capable of receiving an image without using physical wiring has recently been proposed. When presenting an image on a projector of this type, a PC transmits the image via a wireless communication means. For example, when presenting the image signal on the desktop of a PC as in a conventional way, the PC transmits image data obtained by periodically capturing the desktop (acquisition of desktop screen data from a video memory).
In image presentation performed by transmitting an image from the PC to the projector via the wireless communication means, presented successive images may contain the motion of an object such as movement of a pointer by a mouse operation. In this case, presented successive images may not appropriately express the motion depending on the frequency at which capturing is performed. Thus, upon detecting a motion, an image is captured and transmitted, so an image properly expressing the motion can be presented. In other words, when a motion is detected, the frequencies of capturing and transmission become higher than normal.
Recent projectors include an increasing number of pixels of projectable image data. The above-mentioned image presentation via the wireless communication means sometimes uses image data of many pixels. In the arrangement in which the image data transmission frequency rises upon detecting a motion, the transmission quantity per unit time increases. This may increase the traffic in the transmission channel. Increasing the traffic causes a transmission delay of image data to be presented, and a so-called frame drop in which images presented by the projector become discontinuous. As a result, presented successive images may not properly express the motion of an object or the like, impairing the operational feeling experienced by the user.
To solve this problem, for example, Japanese Patent Laid-Open No. 2005-257948 discloses a method of avoiding a transmission delay generated by frequent image updating when a pointer moves. For this purpose, only coordinate information is transmitted for the movement of the pointer, and an image output apparatus renders the pointer at corresponding coordinates.
The method in Japanese Patent Laid-Open No. 2005-257948 can achieve efficient image transmission upon updating a pointer position. However, when a partial object such as a window within the screen is updated, this method may not be able to efficiently transmit an image.